The present invention relates to calibration of images and more particularly, but not exclusively to an apparatus and method for calibration of radiographic images.
In the interpretation of images such as radiographic images, various approaches are known for differentiating between structures which appear in such images.
A major difficulty encountered when interpreting radiographic images is that the body is three dimensional. However, even if the patient is positioned is a known distance from the radiographic camera, the image plane may vary according to an organ or bone of interest. That is to say, the camera may zoom-in or zoom-out, so as to focus at the organ or bone of interest. Consequently, there arises a need to know the scale of the resultant radiographic image, in order to identify the organ (or bone) of interest, accurately estimate the bone dimensions, etc.
U.S. Pat. No. 4,506,676, to Duska, entitled “Radiographic localization technique”, filed on Sep. 10, 1982, describes an adhesive, flexible tape which includes radiopaque dots. The tape is applied to a patient to identify an area of interest, and the image of the dot appears in the x-ray photograph as a pointer to the area.
U.S. Pat. No. 3,812,842, to Rodriguez, entitled “Method for locating blood vessels for catheterization”, filed on Jan. 18, 1973, describes an indexing scale which includes markers that are visible in x-ray photographs. The markers facilitate locating a particular blood vessel relative to the scale in the x-ray photograph, and the arms which support the indexing device are secured to a patient's chest with adhesive tape.
U.S. Pat. No. 5,394,457, to Leibinger, entitled “Device for marking body sites for medical examinations”, filed on Oct. 7, 1993, describes a device for marking body sites for imaging medical examinations. By using multiple markers, two x-ray exposures taken from different directions can be used to determine the spatial location of any desired point. The marker has a head with a cavity for receiving a substance which exhibits high contrast, and in one embodiment, a fixture which supports the marker is attached to the skin with an adhesive.
U.S. Pat. No. 5,469,847, to Zinreich, entitled “Radiographic multi-modality skin markers”, filed on Feb. 28, 1994, describes an adhesive surface marker with a cavity for receiving imaging materials. The surface marker contains an x-ray opaque gel, such as barium sulfate, which is sealed on all sides by an outer casing. The use of multiple markers provides reference points which allow the geometrical calculation of the precise location of a particular site within a patient's body.
U.S. Pat. No. 7,079,620, to Vaillant, entitled “Method and apparatus for determining a magnification factor a radiographic image”, filed on Mar. 13, 2002, describes a method and apparatus for determining a magnification factor in a radiography device of the type comprising an X-ray source and means for acquiring images placed facing the source.
With Vaillant, the source and the means for acquiring images is mounted so as to rotate about one axis with respect to a support on which an object to be X-rayed is intended to be positioned.
The method and the apparatus implementing the method comprises: acquiring two images corresponding to two different angular positions of the source and of the recording means with respect to the support; identifying on these images projections of one or more points of the X-rayed object; and determining the magnification factor of at least one of the images, first, as a function of the angular displacement of the source and of the recording means between the acquisitions of the images in question and, secondly, as a function of the positions on these images of the identified projections.
However, such solutions are not accurate enough, too cumbersome, or are inconvenient.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system devoid of the above limitations.